The patch itself LGTM Though sometimes I muse about whether we need NR 1.8.2 Formatting text in it's current state at all. Why do we explain some markup-commands explicitely and others not? They are all listed with examples in NR A.11 Text markup commands!
An alternative would be to improve examples in the markup-commands where needed (as this patch does for fill-line) and, after explaining what markup is and how to use it, simply point to NR A.11. We already do similiar for markup-list-commands. https://codereview.appspot.com/583340043/
